Inks are dyes which are obtained by dissolving the dyes in suitable solvents. There are organic and in-organic dyes. There are both natural and synthetic dyes. The old archival materials were written by black carbon inks, iron gall inks etc. But in the modern times, aniline inks took a took root in writing on paper. Aniline inks are organic inks and it gets dissolved in water. Therefore one should be very careful in restoring the documents written by aniline ink. If the aniline ink is soaked in water what happens? The ink gets dissolved. The ink can be revived. But where ever the ink blotted the colour of aniline ink will be revived. We may not be able to read the old writings. This can be done by the application of lemon juice. The letters cannot be regenerated by ammonium sulphide, tannic acid, potassium ferro cyanide as it does not contain any iron in the ink.
If any method is available to regenerate the aniline ink kindly let me know by commenting below in the comments section.